A little knowledge about shadows

1. What is a shadow? Light travels in a straight line, and the object in front of the light source blocks the light, and a dark area called a shadow is formed where the light cannot shine. The reason why we see this area is dark is because the light can't reach the back of the blocked object and can't be reflected into our eyes.

An object can cast shadows of different shapes. When the object is close to the light source, the shadow is larger because the object blocks a lot of light. As the object moves away from the light source, the shadow becomes smaller because the light blocked by the object decreases. If you rotate an object, you will get different shapes of shadows.

The edge of the shadow may be clear or blurred. When an object is close to a place where a shadow is cast, such as a wall, the edge is clearly visible. When the object is far away from the place where the shadow is cast, the edge will become blurred. Sometimes the middle part of the shadow is darker than the edge, the middle part is called umbra, and the brighter area is called penumbra. This shadow will appear when the light source is large. In order to make all parts of the shadow equally dark, the light source must be small.

The shadow outside depends on the weather. In sunny, cloudless and sunny weather in Wan Li, the shadows are clear and dark. When the weather is cloudy and gloomy, it is difficult to see the shadow, because the sunlight is scattered by the tiny particles in the cloud and emitted in many directions, which means that the shadow is brighter than usual, so it is not easy to see.

2. The application of shadows by human beings has been very useful to human beings since ancient times. The movement of shadow has its fixed pattern, so we can predict the size and position of shadow. When the earth rotates around its axis, everything on the earth's surface is illuminated by the sun. Mountains, trees and buildings all have shadows, but the position of shadows changes constantly throughout the day. As the position of the sun changes, the shadow moves from one side of the object to the other. In the early morning and evening, the sun in the sky is very low, and the shadows are very long at these times. At noon, the sun is high in the sky and the shadow is very short. The ancients found that the passage of time could be marked with a note, so they invented a sundial to let people know the local time.

3. The color of the shadow The color of the shadow depends on the light reflected by the shadow projection, and then the light blocked by the object is deducted. For example, a white wall reflects white light (in fact, white light contains various colors), so it looks white. When a part of the white light is blocked by an object, the light projected by the object on the wall becomes less, so the shadow part looks darker than the original wall.

If the object selectively blocks the light, the shadow will show different color changes instead of simple brightness changes. There are two possibilities as to how to selectively block the light. First of all, the object itself is selectively transparent (such as colored glass), so it will change the color of the shadow. Secondly, there are more than one light source and different colors. The object only covers part of the light source. For example, if two light sources, red light and green light, are installed in different positions in the environment, the same object will cast shadows of two different colors, red and green, because it is illuminated by both red light and green light, it will appear yellow.

2. Knowledge about shadows

1. What is a shadow? Light travels in a straight line, and the object in front of the light source blocks the light, and a dark area called a shadow is formed where the light cannot shine.

The reason why we see this area is dark is because the light can't reach the back of the blocked object and can't be reflected into our eyes. An object can cast shadows of different shapes.

When the object is close to the light source, the shadow is larger because the object blocks a lot of light. As the object moves away from the light source, the shadow becomes smaller because the light blocked by the object decreases.

If you rotate an object, you will get different shapes of shadows. The edge of the shadow may be clear or blurred.

When an object is close to a place where a shadow is cast, such as a wall, the edge is clearly visible. When the object is far away from the place where the shadow is cast, the edge will become blurred.

Sometimes the middle part of the shadow is darker than the edge, the middle part is called umbra, and the brighter area is called penumbra. This shadow will appear when the light source is large.

In order to make all parts of the shadow equally dark, the light source must be small. The shadow outside depends on the weather.

In sunny, cloudless and sunny weather in Wan Li, the shadows are clear and dark. When the weather is cloudy and gloomy, it is difficult to see the shadow, because the sunlight is scattered by the tiny particles in the cloud and emitted in many directions, which means that the shadow is brighter than usual, so it is not easy to see.

2. The application of shadows by human beings has been very useful to human beings since ancient times. The movement of shadow has its fixed pattern, so we can predict the size and position of shadow.

When the earth rotates around its axis, everything on the earth's surface is illuminated by the sun. Mountains, trees and buildings all have shadows, but the position of shadows changes constantly throughout the day.

As the position of the sun changes, the shadow moves from one side of the object to the other. In the early morning and evening, the sun in the sky is very low, and the shadows are very long at these times.

At noon, the sun is high in the sky and the shadow is very short. The ancients found that the passage of time could be marked with a note, so they invented a sundial to let people know the local time.

3. The color of the shadow The color of the shadow depends on the light reflected by the shadow projection, and then the light blocked by the object is deducted. For example, a white wall reflects white light (in fact, white light contains various colors), so it looks white. When a part of the white light is blocked by an object, the light projected by the object on the wall becomes less, so the shadow part looks darker than the original wall.

If the object selectively blocks the light, the shadow will show different color changes instead of simple brightness changes. There are two possibilities as to how to selectively block the light. First of all, the object itself is selectively transparent (such as colored glass), so it will change the color of the shadow.

Secondly, there are more than one light source and different colors. The object only covers part of the light source. For example, if two light sources, red light and green light, are installed in different positions in the environment, the same object will cast shadows of two different colors, red and green, because it is illuminated by both red light and green light, it will appear yellow.

3. Knowledge post about what is "shadow"

Simply put, it is like this: Shadowwood is also called Sakura (Gall) wood, which literally means a diseased tree with a tumor.

Shadow refers to the wood where trees have nodules or cherry blossoms, which is called shadow. Many kinds of trees can produce shadows, such as birch shadow, camphor shadow, nanmu shadow, pear shadow, maple shadow and so on.

Shadow trees are mostly born in roots, and there are fewer cadres. Shadow wood is mostly staggered, twisted and rotated with fine patterns, with diverse textures, very beautiful, varied and different styles. Common textures include grape grain walnut pattern, landscape pattern, tiger skin pattern, sesame pattern and raindrop pattern.

The value of shadow wood is firstly its texture, and secondly its wood grade. Generally speaking, the order is this: of course, the good grain and color of mahogany hardwood firewood are also important factors in its value. The denser the pattern, the more "faces" (bird eyes) the better. Shadow wood is generally used for surface decoration of furniture and utensils, or small utensils, such as box stationery.

You can make mosaics after slicing. Due to the limitation of the size of the material itself, there are not many large objects made.

Of course, utensils can also be made from the natural shape of huge nodules on the trunk of fast-growing trees with large DBH. The appearance is clean, with no or slight artificial modification, such as cherry wood pen container painting and pen washing. Shadow wood is mostly produced in Southeast Asia, and China is mainly produced in Yunnan, Liaodong, Sichuan and Shanxi.

The above text is combined with online introduction and personal understanding. Due to my limited experience and level, please correct me if there is anything wrong, and welcome everyone to add! []。

4. Know little about exploration

1: A must-have for adventure, a lighter! It doesn't matter if you don't bring food A lighter is a must. If you meet wild animals at night, you can drive them away. If it is cold, you can make a fire to keep warm. If you hunt food, you can use it to cook (if you get shot, you can also disinfect surgical instruments, which are in the movie).

2: Hold your breath and play dead when you meet a bear! Bears are not interested in dead things!

Wearing a mask on the back of the head can effectively prevent tigers from attacking, because tigers don't attack people head-on!

4: Most snakes don't take the initiative to attack people, except cobras and rattlesnakes, but usually there are such snakes in the rainforest!

5. Mung bean soup and soybean milk food and drink have detoxification effect. For example, eating toxic food and mung bean soup in the wild can effectively alleviate the toxicity, and you can drink it immediately to save yourself!

6. Wet towels can effectively avoid burns in the hot sun.

7: Aloe, cactus and other plants can also effectively detoxify, and the effect is better than mung bean soup when rescuing people who take poison. If your cat accidentally eats poisonous mice, you can mash them and give first aid. But the grass mud is too thick for poisoned animals to drink, so they can drink egg white and boil licorice.

8. Aloe and cactus have a good detoxification effect. If your body is bitten by poisonous insects, you can slice aloe or cactus and apply it to the injured surface.

It is not suitable to enter the dense forest in the morning. In the morning, there is too much carbon dioxide and insufficient oxygen in the forest, which is easy to lead to hypoxia, and people with weak constitution are easy to faint.

9. Water necessary for survival in the wild. If there is no water, we must first find wild fruits that can be used. If there are no wild fruits, the worst way is to borrow plants, put plastic bags on the branches and leaves of green plants, tie them tightly, and use photosynthesis and evaporation to form water droplets inside the bags. Although meager, it can save lives.

10: If you get lost, you can refer to the sun and shadow. The sun and shadow are located in the north of the Tropic of Cancer, and the shadow will never only face south, that is, at least in the area north of the Yangtze River: at sunrise, the shadow faces west, and at sunset, you can know the north and south according to the upper north, lower south, left west, right east; The shadow points northwest in the morning, northeast in the afternoon and north at noon.

1 1: You can see plants when there is no sun, and the fabric is phototropic. You can judge the position of the sun by the orientation of the azimuth, so as to judge the direction according to the above method.

12: It can be judged by the moon at night. The moon does not point to the shadow, but points to the arc. You can see the moon in the middle of the night, which proves that it is the first to fifteenth day of the lunar calendar. At this time, the moon gradually becomes round from the stationary semicircle to the other side. This stationary semicircle points west from the first day to the fifteenth day, and faces east from the sixteenth to the thirtieth.

13: Don't hide in big trees and tall buildings during a thunderstorm.

14: It's best to take off and land with both feet when touching the ground wire, and skip this range.

15: When encountering thorns, you can open the way through the knife.

16: You can use a rope as a tool when climbing a mountain.

17: Learn more about animals and plants.

5. The main content of Andersen's fairy tale "Shadow Story"

This is the original text of the Baidu library "Shadow":

Introduction: This was written by Andersen in the summer of 1846 in Naples, a coastal city in southern Italy.

The climate there is very hot, especially in summer. This "heat" may be the "inspiration" that prompted the author to write this story. But the story itself is "cold", which makes people feel creepy, but it is not impossible in real life.

That scholar, the so-called intellectual, is bound to be drowned by his own shadow and become an innocent victim, but he doesn't realize it himself.

This also shows how keen Andersen, who is kind, naive and kind, is in observing life-he is a great writer!

Later, this fable was first published in New Fairy Tales.

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Thoughts and feelings:

This fairy tale describes a magical story: a scholar lost his own shadow, and later the shadow became a human form, defrauding the scholar of his social identity, and finally framed the scholar to death with trickery. The story seems absurd, but in fact it is thought-provoking, which embodies the author's keen insight and deep thinking on social reality and human nature.

The story of a scholar murdered by his own shadow symbolizes Andersen's embarrassing situation distorted by secular people and vulgar enthusiasm, and also shows his deeper loneliness.

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Feeling:

Under the sunlight, the shadow always follows the shape and looks gloomy and disturbing. Although the shadow has no independent life, it changes endlessly, and it is inevitable that it will get carried away for a long time, thinking that it can travel around the world without being attached to its master. He said to his master, let's pretend to be friends and develop together elsewhere. They came to a country where the king was recruiting a husband for the princess. Shadow boldly applied for the job and was selected, so he began to hate his master's old and ugly appearance, so he asked the king to put him in prison. On the eve of the wedding, the shadow worried that the host would destroy the game and sent someone to poison the host. and then

The endings of fairy tales are mostly nothing more than: "From then on, the shadow and the princess lived a happy life." However, not this time. The ending should be left to the readers to think for themselves. Answer 1: Since the owner is dead, how can the shadow exist alone? The shadow should disappear, so that everything is like a spring dream, without a trace. Answer 2: The plot of the shadow was exposed and was appropriately punished. Answer 3: Reflection, are we all creating such a shadow? Or, life is the process of the shadow murdering the master?

Shadows symbolize our fantasies and desires. In order to realize our fantasies and satisfy our desires, we travel around the world and learn the necessary knowledge and skills. In this process, we gradually become secular and become a model welcomed by the society. External roles, status, relationships, and achievements are enough to make people forget themselves and even hate the occasional questioning heart. The trick of murdering the master is easy to succeed. And the result? The streets are full of shadows. Among the philosophers of the Ming Dynasty, some people claimed that the streets were full of saints. This really needs a special eye, but what the sage said is too vague. In my opinion, the streets are full of shadows, which may be closer to the truth.

6. Excuse me, who has common sense of reasoning?

People generally become stiff within 30 minutes to 2 hours after death, and will become stiff after 9 to 12 hours.

After 30 hours, it will continue to be stiff, then soften and return to its original state in about 70 hours. Usually, this is the case, but if the ambient temperature is higher than 35 degrees, the stiffness and softening will accelerate and it will recover in 24 hours.

After strenuous exercise before death, protein is easy to solidify in the body, and will become stiff faster than usual after death. Suicide is when a gun is pointed at the head, which will leave hot marks around the bullet hole and the color of the surrounding skin will deepen. ※.

Moreover, the hole in which the bullet enters is smaller than the hole out, and there is less blood flow. Under normal circumstances, only suicide will leave burn marks. If the lungs are perforated, even if you want to breathe, you can't breathe smoothly because the lungs can't expand, which will lead to suffocation and death. ※.

You can probably struggle painfully before you die 10~ 15 points. Drowning: slight water stains in the mouth, dilated pupils, bleeding on the mucous membrane of the eyes, and rupture of the eardrum due to water pressure, leading to bleeding. ※.

Poisoning: the lips turn purple or black first, and then other parts of the body will also appear this phenomenon. Sometimes eyes stare, hands clench fists, waist and legs curl up, etc. ※. Choke to death: there is a deep purple imprint on the throat. When it hurts, the pupil expands and the tongue sometimes sticks out, showing purple-black. ※.

Cleaning the wound with tea to neutralize toxicity is the best way to deal with sea snake bites, because tannins contained in tea can detoxify. In addition, the person in charge of sucking out the poison should also gargle with tea to prevent poisoning. ※. In case of food poisoning, mung beans can be ground and washed to temporarily remove toxicity. ※.

When salt is mixed with acidic detergent, it will produce toxic gas. The skin of the deceased was pink with some spots from the inside out, which was obviously caused by sodium hydroxide poisoning. ※. If the poison be in the capsule. ※.

It takes at least 15 minutes to show toxicity. It is best to gargle with something containing protein, such as milk.

PS: Potassium cyanate is insoluble in cold water. ※. The surgeon will leave a deep and obvious mark on the index finger, which is caused by frequent dressing. The hair of the deceased was slightly burnt and the muscles of the whole body were extremely stiff, which was the characteristic of high-voltage electric death. ※.

The scald caused by the current flowing into the body from the fingertips will turn the fingers gray. Eating potassium hydroxide may lead to suffocation and death (potassium hydroxide has almond flavor). ※. ※.

If you poison a flower, the flower itself should wither first. On the surface, it seems that it is a "suicide" death by biting the tongue, and sometimes it is a convulsion caused by inhaling poisonous gas or swallowing poison. ※. ※.

There are many kinds of poisonous bacteria, some of which release poisonous toxins. Poisonous bacteria can also be used as medicine, but they are also poisonous, so you'd better not eat them. ※.

Carbon dioxide poisoning: the gas around people contains more than 20% carbon dioxide, so people will have severe convulsions after inhalation, and they will bite their tongues in a few seconds and die of cold. Carbon dioxide is heavier than air, so it will sink in a certain space. ※.

If the spasm is caused by massive bleeding, a rope must be tied around the wound to stop bleeding and prevent excessive bleeding. Next, massage your heart. If a person's internal organs are broken, there will be a special smell of internal organs. ※. ※.

A big echo in the cave means there is no road, and a small echo means there is still a road. Sodium sulfide (bleach) can detoxify potassium hydroxide. ※. ※.

The surface of pearl is calcium carbonate, which is most afraid of acid corrosion. Therefore, when touching precious pearls, be sure to wear gloves or wrap them with handkerchiefs. If you don't use them, pearls will encounter oil stains on your hands and their luster will disappear faster. The luster life of pearl surface is 30~40 years at most, and then it will fade slowly.

When the corpse is buried in the soil, so that the corpse can't touch the air, the decomposition speed of the corpse will be normal 1/8, and it will be slower in water. Generally, people who have been missing for more than seven years will be confirmed dead, and those who have disappeared due to natural disasters or disasters will be confirmed dead for more than one year. ※. ※.

Hitting a person's head with a blunt instrument may even cause a file tear. Usually, there will be no blood spilling from the first blow, but there will be scars around the wound. ※. Only when the second blow is in the same place will the blood come out.

Upper and lower lip mucosal bleeding, neck epidermis peeling, skin peeling bleeding, conjunctival bleeding, etc. Indicating strangulation. If the deceased is strangled and hit on the head with a blunt instrument, it will cause serious intracranial injury and respiratory system failure and die. ※. ※.

Eating a certain amount of sodium nitrite will also kill people. Only a small amount of toxicity enters the bone marrow in acute poisoning. ※.

DNA fingerprinting is highly individual-specific, which unifies the consistency between different tissues of an individual. Its repetition rate is one in a billion, which is similar all over the world. Bats in caves usually inhabit within 300m (100m) of the entrance. ※. In the forest, it is impossible to hear someone shouting from one direction, but from all directions. Sprinkling salt on snow can accelerate the melting of snow, so footprints can be formed after snow. In the northern hemisphere, the sun is in the east around 6 o'clock local time, which is about 12 hour. ※

In the north and south, the sun is in the east around 6 o'clock, in the zenith * north around 12, and in the west around 18. This can also roughly determine the direction.

If the watch of the person in distress is damaged or the time is inaccurate, you can use the compass to determine the time first. First, measure the azimuth of the sun, divide it by the number of angles when the sun turns 1 hour 15, and add 1 to get the local time. ※.

For example, the azimuth of the sun is 180 and the local time is180 ÷15+1=13. Orientation with wooden stick shadow: put a straight stick or wooden stick so that it is perpendicular to the ground, and put a small stone at the vertex of the shadow of the straight stick. About 10 minute, when the vertex of column shadow moves to *, put a small stone to connect * and * into a straight line. ※. This straight line points to the east-west direction, and the direction perpendicular to the * * line is the north-south direction (the end facing the sun is south, and the opposite direction is north). During the day, if the clouds are thick, you can't see the sun. ※. At this time, we can also use the characteristics of natural objects to identify the direction.

1。 In the wilderness, the leaves of independent trees are dense in the south and thin in the north.

2。 It can be seen from the sawed stump that the tree rings are sparse on the south side and dense on the north side.

3。 In the northern hemisphere, moss on tree trunks or rocks usually grows under backlight.